1. Field of the Invention
This invention relates to the field of optoelectronic devices and, more specifically, to light-sensitive semiconductor devices for detecting the wavelength of incident electromagnetic radiation,
2. Description of the Prior Art
In the past, many semiconductor devices, such as the photodiode, have been developed which are readily excited by photons to vary the electrical conductivity thereof. Thus, when the photons of electromagnetic radiation in the visible or infrared spectrum are absorbed by an appropriate semiconductor, a change of conductivity results due to the holes and electrons created by the absorbed photon energy. Such semiconductor devices have been operated in a photovoltaic mode wherein no external electrical bias is provided, and wherein a change in voltage across the device results from the creation of excess electron-hole pairs due to the absorption of photons. Radiation-sensitive semiconductor devices can also be operated in a photoconductive mode wherein a reverse bias is applied across a junction of the semiconductor device in order to create a depletion layer in which carriers are generated by the photons absorbed from incident radiaton. When a reverse bias is applied, the response time of the semiconductor device is decreased since the electric field generated by the reverse bias decreases the transit time of the carriers conducted through the semiconductor to the respective terminals thereof.
It is also well known that the light absorption of a semiconductor light detector is a function of the thickness and absorption coefficient of the semiconductor and of the wavelength of the incident light. An example of a device utilizing this principle is disclosed in U.S. Pat. No. 3,452,204 wherein the thickness of a reverse-biased photodiode is appropriately established so that only incident radiation of a relatively narrow bandpass is detected. While such a device is responsive to a selected narrow frequency band, this reference does not disclose a method or apparatus for measuring the frequency or wavelength of incident radiation.
With the increased utilization of radiation-controlled devices such as lasers, there has resulted an increasing need for a simple, but accurate, means for detecting the wavelength of incident radiation. Wavelength measuring devices in the past have employed multiple light filters and detectors which are either exceedingly complex or lack the sensitivity required for many applications.